1 Field of the Invention
This invention relates to plate-and-fin heat exchangers and, more particularly, to arrangements for improving the structural integrity of such apparatus when subjected to transitional operating conditions.
2. Description of the Prior Art
Devices have long been known for utilizing heating or cooling fluids for the purpose of limiting temperature differentials and thermal gradients. Arrangements are also well known in the prior art which control the flow of a heating or cooling fluid to limit the effect thereof during transitional operating stages and to maintain operating temperatures within preselected ranges. An example of the latter is the thermostat commonly found in an automotive cooling system. This virtually blocks flow of a coolant to the engine when the engine is cold and, during the normal operating phase, variably restricts the coolant flow in accordance with the desired steady state operating temperature of the engine, the boiling point of the coolant or particular constituents thereof, and the demands of related equipment, such as a heater which draws heat from the engine coolant to heat the passenger compartment.
U.S. Pat. No. 2,658,728 of Evans, Jr., U.S. Pat. No. 2,986,454 of Jewett, U.S. Pat. No. 2,615,688 of Brumbaugh, and U.S. Pat. No. 3,504,739 of Pearce are examples of disclosures involving the use of an intermediate fluid in heat exchangers generally of the tube and sheet type to provide physical separation between, and reduce the thermal gradients and shock in respective chambers or other heat transfer structure containing the respective heat exchange media.
The Ohlander U.S. Pat. No. 2,661,200 discloses an arrangement for introducing a gas into a heat sensitive region of a refractory nozzle to limit the maximum temperature of the protected region. This patent, as well as the aforementioned Jewett and Pearce patents, also discloses the use of the related apparatus for pre-heating the tempering fluid.
Insofar as is known, however, none of the prior art arrangements disclose the utilization of a gaseous fluid for heating or cooling selected portions of a heat exchanger during the starting up or shutting down transitional phases between steady state operating conditions and shutdown. In particular, this concept has not previously been applied to plate-and-fin heat exchanger manifolds in the manner of the present invention.